Process for electrolytic chromium-plating steel strips without a bluish tint while using two or more plating tanks



Aprll 1967 HIROMU UCHIDA ETAL 3, 0

PROCESS FOR ELECTROLYTIC CHROMIUM-PLATING STEEL STRIPS WITHOUT A BLUISHTINT WHILE USING TWO OR MORE PLATING TANKS Filed Aug. 7, 1963 3Sheets-Sheet 1 k) g L 31 L. a; Q Q a {Q I\ & *w

1 N VEN TORS BY 74/(50 ADACH/ umv TSUJ/MOTO April 1967 HIROMU UCHIDAETAL 3,316,160

PROCESS FOR ELECTROLYTIC CHROMIUMPLATING STEEL STRIPS WITHOUT A BLUISHTINT WHILE USING TWO OR MORE PLATING TANKS Filed Aug. 7, 1963 3Sheets-Sheet 2 A M Q;

JUN W 9 April 25, 1967 IROMU UCHIDA ETAL 3,316,160 PROCESS FORELECTROLYTIC CHROMIUM-PLATING STEEL WITHOUT A STRIPS BLUISH TINT WHILEUSING TWO OR MORE PLATING TANKS Filed Aug. 7, 1963 3 Sheets-Sheet 5 YNABU BY 741645! #404 A Tram/5w.

United States Patent 3,316,160 PROCESS FOR ELECTROLYTIC CHROMIUM-PLAT-ING STEEL STRIPS WITHOUT A BLUISH TINT WHILE USING TWO OR MORE PLATINGTANKS Hiromu Uchida, Osamu Yanabu, Takashi Hada, Takeo Adachi and JunTsujimoto, all of Hyogo-ken, Japan, assignors to Fuji Iron & Steel Co.,Ltd., Tokyo, Japan Filed Aug. 7, 1963, Ser. No. 300,589 Claims priority,application Japan, Aug. 16, 1962, 37/155,474; Dec. 3, 1962, 37/54,480 8Claims. (Cl. 204-28) This invention relates to a process for producingelectrolytic chromium-plated steel strips using more than two platingpaths or plating tanks and, more particularly, to an economical andadvantageous process of this type in Which the electrolyticchromium-plated steel strip is produced without a bluish tint.

In the usual case, when a steel strip or wire is electrolytically platedwith chromium using only one plating tank, plating having a lustroussilvery white color is obtained easily. However, when the number ofplating tanks is increased to two or more, and if the plating in andafter the second tank is effected using the same procedure as in thefirst plating tank, the surface of the steel strip will become bluishand lusterless. In turn, this will interfere with the color quality ofpaint coated thereon, thus lowering the value of the plated steel stripas saleable merchandise. The same phenomenon occurs using only oneplating tank, if the plating paths are increased to two or more.

The cause of the plated surface becoming bluish, when plating iseffected using two or more plating tanks or paths, is not clear.However, it has been surmised that a film of a complex chromium oxide isproduced at the surface of the steel strip as it emerges from the firsttank and may be the cause of this phenomenon.

As a result of experiments in an attempt to solve the problem of thebluish tint, the invention process has been developed and by thisprocess chromium-plated steel strips without a bluish tint may be easilyand advantageously obtained even when there are two or more platingtanks, or two or more plating paths in a single tank. The essence of thepresent invention resides in using certain specific treatment conditionswithin successive tanks or paths as cept the first tank or path.

More specifically, in accordance with the present invention,electrolytically chromium-plated steel, without the bluish tint, isprovided by moving the steel strip through more than two tanks or paths,and in each of the plating tanks or paths after the first, imparting tothe steel strip a cathodic treatment under low current density succeededby chromium plating in the same path or tank.

For example, to remove the film causing the bluish tint, the presentinvention may rely upon the known Surgeant bath for the chromium platingprocess. In this case the cathodic treatment is effected by maintainingthe steel strip negative with a current density of about 0.1-l0 a./dm.for 0.01 to 3 seconds. The eificiency of removing the said bluish tintwill be insufiicient if the current density is greater than about a./dm.or less than 0.1 a./dm.

In accordance with the invention it has been found that, when suchcathodic treatment and chromium plating are effected successively withinthe same plating tank, or along the same plating path, an electrolyticchromiumplated steel without the bluish tint may be obtained even ifthere are two or more plating tanks used or two or more plating paths,and the steel strip obtained will have a 2 lustrous silvery white colorsuch as is obtained by using only one plating tank or path.

The present invention is applicable to plating using vertical type ortanks of a horizontal When using vertical tanks, plating is effected ineach tank during the downward path of the strip or wire and, after thelatter passes over the sink roll, in the upwith low current densitybefore the plating. An electrolytically chromium-plated steel stripwithout a bluish tint may thus be obtained advantageously by using morethan two plating tanks.

When the of small holes. In this case the steel strip or wire may beprovided with a preliminary plating of a thin layer of. copper, nickelor alloys thereof.

The present invention is based upon the discovery that plating tank,

path in each path after the first plating path.

A feature of the invention plating tanks, in each tank after the firstthe downward manner as mentioned above.

The material used for the shielding plate or plates must be dielectricand corrosion resistant, such as, for example, vinyl chloride or thelike.

For an understanding of the principles of the invention the followingdescription of typical embodiments thereof, as illustrated in theaccompanyin drawings and in accordance with the examples givenhereinafter.

In the drawings:

FIG. 1 is a somewhat schematic and diagrammatic side elevational viewillustrating the practice of the present invention using verticalplating tanks;

FIG. '2 is a somewhat schematic and diagrammatic side elevationillustrating the practice of the invention using horizontal platingtanks;

FIG. 3a is a partial elevational view illustrating one of the shieldingplates or members in association with the strip to be treated;

FIG. 3b is a sectional view taken on the line AA of FIG. 3a; and

FIG. 3c is a sectional view taken FIG. 3a.

Referring to FIG. 1, the steel strip or wire is led from an uncoilerroll 1 through pinch rolls 2, a welder 3, and a driving and tensioningroll assembly 4, the strip being led into an electrolytic degreasingtank 5. From tank 5 the strip is led through a water tank 6, where thestrip is washed, an electrolytic pickling tank 7 and a waterwashing tank8 where the strip is again washed. The strip is then led into the firstplating tank 9. In tank 9, electrolytic chromium plating is effected ina downward path 10 and an upward path 11.

In accordance with the invention, the steel strip is then led into asecond plating tank 12 which is provided with the aforementionedshielding means A positioned so as to cover the upper portion of thedownward path 13. Within the portion of the path covered by theshielding tank A, the strip is given a cathodic treatment which iseffected by the relatively small electric current flowing through thesmall holes in the shielding plate. In the same tank, and after passingover the sink roll, the strip is electrolytically chromium-plated in theupward path 14.

The treatment given to the strip in tank 12 is repeated in each of thetanks '15, 16 and .17, utilizing shielding plates or casings B, C and Dcorresponding to the plate or casing A.

The steel strip or wire emerging from the tank 17 is then passed througha washing tank 18, a chemical treating tank 19, and a hot Water washingtank 20. The strip is then sprayed with oil in an emulsion-oiling tank21 and coated with a predetermined amount of oil film by means of thesqueezing rolls 22. The steel strip is then dried in drying furnace 23and coiled on a coiling roll 25 after passing through tensioning anddriving roll assembly 24.

In the schematically illustrated electrical supply for the apparatus,components 26 and 27 are D.C. sources for the electrolytic degreasingand electrolytic pickling. D.C. sources 28 through 32 are used for eachof the plating tanks 9, 12, 1'5, 1 6 and 17, respectively.

FIG. 2 illustrates the invention as used with horizontal plating tanks.In this case the steel strip or wire is led from the uncoiler means 33into an electrolytic degreasing tank 37 after passing through pinchrolls 34, welder and a tension and driving roll assembly 36. Leavingtank 37, the strip is passed through a brush scrubber 38, anelectrolytic pickling tank 39, a brush scrubber 40, and over an electricpotential applying conductor roll 41 into the first plating tank 43.Roll 41 is connected to the negative terminal of D.C. source 66. In tank43 electrolytic plating is effected by means of an electrode 42,connected to the positive terminal of source 66.

The strip of wire is then led into the second plating tank 46 over aconductor roll 44 connected to the negative terminal of source 67.However, in tank 46, cathodic treatment using a very small current iseffected at the entrance portion to the electrode 45 by means of ashielding plate A which may be the same as previously described. Afterpassing through the electrode 45, the strip is electrolytically platedin the usual manner. Electrode 45 is connected to the positive terminalof D.C. source 67.

In each of the succeeding plating tanks 49 to 52 and 55 cathodictreatments followed by electroplating are effected in the same manner asmentioned for tanks 46. In advance of entering each of the succeedingtanks 49, 52 or 55, the strip or wire passes over a conductor roll 47,50 or 53, respectively, connected to the negative terminal of a D.C.source 68, 69 and 70, respectively. (Electrodes 48, 51 and 54 areprovided in the respective tanks 49, 52 and 55, and are connected to therespective positive terminals of the sources 68, 69 and 70. In eachcase, the shielding dielectric and corrosion resistant plates B, C and Dare positioned to enclose the strip as the strip enters the electrodes48, 51 and 54, respectively.

On leaving tank 55, the strip of wire passes over the on the line B-B ofroll 56, which is connected to the negative terminal of the D.C. source66, and then into a washing tank 57 after which the strip passes througha chemical treating tank 58 and a hot water washing tank 59 before it issprayed with oil in the emulsion oiling tank 60 and coated with apredetermined thickness of oil film by means of pressure roll 52. Thesteel strip is then dried in the drying furnace 63 and coiled on arecoiler 65 after passing through the driving and tensioning rollassembly 64.

The D.C. current sources for the degreasing tank 37 and the picklingtank 39 are illustrated at 71 and 72.

Referring to FIGS. 3a, 3b and 3c, the construction of the shieldingplate A may be seen. Each shielding plate A, which is alsorepresentative of the shielding plates B, C and D, is a fiat rectanglein cross-section and has a substantial lateral and longitudinal extentwith respect to the strip S. One wide surface or wall of each plate orcasing A is imperforate, while the opposite parallel surface is formedwith the very small perforations 73. These very small perforationsgreatly decrease the current flow to the strip S, while the latter ispassing through the shielding plate A.

The following specific examples are given to illustrate how theinvention may be applied in practice:

Example I A steel strip having 0.25 mm. thickness is electrolyticallydegreased at 30 C. in a degreasing solution containing 5% caustic sodaand 3% sodium silicate, with a current density of 40 a./dm. for twoseconds. It is then washed by water and is electrolytically pickled in a5% solution of sulfuric acid with a current density of 20 a./dm. for twoseconds. It is washed with water again, and while keeping thetemperature of the chromium plating electrolyte, which contains 250g./l. of chromic acid anhydride and 2.5 g./l. of sulfuric acid, at 45C.', it is chromium plated for two seconds in the first plating tank(the vertical type) with a current density of 30 a./dm. The strip isthen subjected to cathodic treatment in the downward path of the secondplating tank (the vertical type) with a current density of 3 a./dm. for0.5 second, and to plating in the upward path with a current density of30 a./dm. for one second.

In the third, fourth and fifth plating tanks (the vertical type) theplating is effected in the same manner as in the second plating tank.Chromium coating of 0.05 micron thickness, having a lustrous silverwhite color, is thus made on the steel strip.

The steel strip is then washed by water and dipped in a 1% chromic acidwater solution at 50 C. for two seconds and after being washed by hotwater, it is oiled by an emulsion-Oiler and is coiled on the recoiler.

Example 11 A steel strip having 0.25 mm. thickness, which has beensubjected to electrolytic degreasing and electrolytic picking in thesame manner as Example I, is plated in the first plating tank (verticaltype) with a current density of 40 a./dm. for one second in each of thedownward path and the upward path, while keeping the temperature of thechromium plating electrolyte, containing 200 g./l. of chromic acidanhydride and 2 g./l. of sulfuric acid, at 50 C. The strip is thensubjected to cathodic treatment in the downward path of the secondplating tank, with a current density of 5 a./dm. for 0.2 second, andthen plated, with a current density of 40 a./dm. for one second, in theupward path.

In the third, fourth and fifth plating tanks, the plating is effected inthe same manner as in the second plating tank, and thus chromium coatingof about 0.06 micron thickness, having a lustrous silver white color, isobtained on the steel strip.

Example 111 A steel strip having 0.25 mm. thickness, which has beensubjected to electrolytic degreasing and electrolytic pickling in thesame manner as Example I, is plated in the first plating tank (verticaltype) with a current density of 30 a./dm. for one second, in both thedownward path and the upward path, while keeping the temperature of thechromium plating electrolyte, which contains 200 g./l. of chromic acidanhydride and 2.0 g./l. of sulfuric acid, at 50 C.

The strip is then subjected to cathodic treatment in the downward pathof the second plating tank with a low current density of about 5 a./dm.restricted by means of the shielding plate, for about 0.1 second andthen plated, with a current density of about 30 a./dm. for about 0.9second. In the upward path the plating is effected, without anyshielding plate, at a current density of 30 a./dm. for about one second.

In the third, fourth and fifth plating tanks the plating acid, at 50 C.It is then subjected to cathodic treatment in the second plating tank(the horizontal type) with a low current density of about 1 a./dm. bypassing through a shielding plate having small holes, on the inlet sideof the electrode, for about 0.3 second, and then plated with a currentdensity of 30 a./dm. after leaving the shielding plate, for about 1.2seconds.

In the third, fourth and fifth plating tanks (the horizontal type)cathodic treatment is effected by using shielding plates on the inletside of the electrode. Plating is then effected in the same manner as inthe second plating tank, and thus chromium coating of 0.05 micronthickness, having a lustrous silver white color, is obtained on thesteel strip.

1. A process for obtaining an electrolytic chromiumplated steel strip orWire having a lustrous chrorninum coating, characterized by the absenceof a bluish tint, comprising the steps of passing the steel strip orwire through more than two plating paths; in the second path and in eachsucceeding path the second path, initially at a low current density of0.1 to a/dm. thereafter, in each plating path, chromium-plating thesteel strip or Wire; and intermediate each plating path withdrawing thesteel strip or wire from the plating solution.

2. A process for obtaining an electrolytically chromiupon the steelstrip or wire to a value which is only a minor fraction of the currentdensity effective during the plating operation; thereafter, in thesecond path and in each of the succeeding paths, subjecting the steelstrip or wire to an electrolytic chromium-plating at normal currentdensity; and intermediate each plating path withdrawing the steel stripor wire from the plating solution.

3. A process for electrolytically chromium-plating steel strip or wireto obtain a lustrous coating characterized by the absence of a bluishtint, comprising the steps of passing the steel strip or wire along morethan two horizontal plating paths each having an activating electrodedisposed therealong; in the second path and in each path succeeding thesecond path, in advance of the: steel strip orwire passing theactivating electrode, passing the steel strip or wire through shieldingmeans formed with a preselected number of very small apertures to reducethe currentflow to the strip or wire to a value which is only a minorfracplating action; in the activating electrode, a normal chromiumplating current flow; and, intermediate each plating path, withdrawingthe steel strip or wire from the solution.

4. A process for obtaining an electrolytically chromium-plated steelstrip having a lustrous chromium coating characterized by the absence ofa bluish tint, comprising or wire through more each tank succeeding thesecond tank, chromium-plating the steel strip or wire; and intermediateeach plating path withdrawing the steel strip or wire from the platingsolution.

5. A process for obtaining an electrolytically chromium-plated steelstrip or wire having a lustrous chromium the absence small value whichis only a minor fraction of the normal plating current density; and inthe upward section of the second tank and of each tank succeeding thesecond tank chromium-plating a steel strip or wire with a currentdensity of a normal value.

for electrolytically chromium-plating a electrode; in the the secondtank, in advance of the steel strip or wire passing the activatingelectrode, shielding the plating operation; in the second tank, and ineach tank succeeding the second tank, as the steel strip or wire passesthe activating electrode, subjecting the steel strip or wire to thenormal current density of the plating; and intermediate each platingpath withdrawing the steel strip or wire from the plating solution.

7. A process for electrolytically chromium-plating steel ond path and ineach path succeeding the second path initially subjecting the steelstrip or wire to a cathodic treatment using a low current density of0.01 to 10 a/dm. in the succeeding portion of the second path and ofeach 5 path succeeding the second path, subjecting the steel strip orwire to normal chromium-plating density; and intermediate each platingpath withdrawing the steel strip or wire from the plating solution.

8. In the process claimed in claim 7, in the initial portion of thesecond path and of each path succeeding the second path, shielding thesteel strip or wire by passing it through shielding means formed with apreselected number of very small perforations to reduce the currentdensity during the cathodic treatment to said low value.

8 References Cited by the Examiner UNITED STATES PATENTS 1,794,973 3/1931 McBride 204-428 2,266,330 12/1941 Nachtman 204-28 2,619,454 11/1952 Zapponi 204-211 FOREIGN PATENTS 727,789 4/1955 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner. T. TUFARIELLO, Assistant Examiner.

1. A PROCESS FOR OBTAINING AN ELECTROLYTIC CHROMIUMPLATE STEEL STRIP OR WIRE HAVING A LUSTROUS CHROMINUM COATING, CHARACTERIZED BY THE ABSENCE OF A BLUISH TINT, COMPRISING THE STEPS OF PASSING THE STEEL STRIP OR WIRE THROUGH MORE THAN TWO PLATING PATHS; IN THE SECOND PATH AND IN EACH SUCCEEDING PATH THE SECOND PATH, INITIALLY SUBJECTING THE STEEL STRIP OR WIRE TO A CATHODIC TREATMENT AT A LOW CURRENT DENSITY OF 0.1 TO 10 A/DM.2; THEREAFTER, IN EACH PLATING PATH, CHROMIUM-PLATING THE STEEL STRIP OR WIRE; AND INTERMEDIATE EACH PLATING PATH WITHDRAWING THE STEEL STRIP OR WIRE FROM THE PLATING SOLUTION. 